This invention refers to a method and equipment for pyrolytic treatment of organic material, such as rubber and plastic wastes, other polymeric wastes, slaughterhouse waste, and other organic wastes.
In a pyrolysis process the organic material is thermally broken down in absence of oxygen at high temperatures of about 500 to 900.degree. C., whereby carbon and hydrocarbon compounds are recovered. Due to the high temperature used in the pyrolysis process it will also be possible to destroy contaminated wastes, without any dangerous exhaust.
There is a lot of pyrolysis methods known in the art, for recovering for instance rejected tires, whereby the tires or rubber waste after size reduction to segments of suitable size are inserted in a big ovenlike reactor for gasification without oxygen supply, which takes place at temperatures from 450 to 600.degree. C. By the pyrolysis process a volatile gas, a so called pyrolytic gas is received, which besides water vapor for instance comprises carbon monoxide, carbon dioxide, paraffines, olefins and some other hydrocarbons, from which pyrolytic gas oil and gas can be recovered. From the solid carbon containing residue, wherein said residue comprises a pyrolytic coke, received in a pyrolysis reactor after the pyrolysis has been carried out, carbon black and/or activated carbon can be produced. The product yield from recovered tires consists substantially of about 20 percent oil, 25 percent gas, about 15 percent steel and other materials, as well as about 40 percent carbon.
A reason why pyrolysis processes hitherto only in very small extent have been used for recovering tires and other rubber material is that the equipment as such requires very big investments and that the price you can get of products which are obtained from rejected tires in such equipment becomes too low in relation to the price you can get of corresponding products produced in a conventional way. Especially concerning the different types of petroleum products, which by a sub-sequent separation step and refining can be produced by the pyrolysis process.
The carbon or the pyrolytic coke which is received as a residue from the pyrolysis process has from an economical point of view proven to be comparable to carbon produced in a conventional way, especially if the carbon obtained by the pyrolysis is further refined to carbon black. Carbon black is used in large amounts as pigment and filler in the plastics and rubber industry.
By condensation of less volatile components in the pyrolytic gas received in the pyrolysis process, so called pyrolytic oil can be obtained, which substantially looks like diesel or light fuel oil but with the difference that it has a relatively high content of sulfur and aromatic hydrocarbons. The high content of sulfur and further occurring impurities can for instance be reduced by filtering and the hydrocarbons compounds can be separated to different fractions by condensation. The temperatures at which oil is condensed from the pyrolytic gas is different depending on the density of the oil but in principle the heavier oil fractions are condensed at temperatures of about 350.degree. C., the middle heavy oils at temperatures of 100 to 350.degree. C. and the light oils at temperatures below 100.degree. C. The condensing oil fractions are led for further storage into special collecting tanks while the remaining noncondensed pyrolytic gas preferably is used as fuel for the recovery equipment.
As mentioned above, some pyrolytic products are so valuable that they can be considered as raw material for further treatment and refining. However, tests have shown that the properties of said pyrolytic products to a great extent are determined already during the pyrolysis process by for instance the temperature, the heating rate, the dwell time in the reactor as well as the cooling rate. Consequently it is desirable to be able to control these parameters very exactly during the present pyrolysis process.
If the coke remaining after the pyrolysis process shall be used as solid fuel screening separates it from steel and glass fiber residue and is led to storage. However, coke which is aimed to be further refined to e.g. carbon black or activated carbon have to be pyrolytically treated in further pyrolysis steps comprising elevation of the temperature to a range of 800 to 900.degree. C. in order to completely remove all possible traces of volatile hydrocarbons from the coke and subsequent temperature degradation.
From U.S. Pat. No. 3,962,045 an equipment for pyrolysis treatment of waste, such as plastics and rubber, is known using recirculating heated pyrolytic gas for heating the waste, whereby the circulating pyrolytic gas is led through a reactor zone in which it is brought to cross a continuous flow of waste passing through the reaction zone. When the gas has passed through the reactor zone a part of the generated pyrolytic gas is led back to a condenser unit to be condensed to liquid phase while another part of the pyrolytic gas is led to a heat exchanger to be reheated and led back through the reactor zone. The coke formed during the pyrolysis process is discharged by means of a screw feeder from the bottom of the reactor zone to a collecting unit. Because the waste is fed continuously through the reactor zone the possibilities to control the pyrolysis process are restricted and the formed coke must from a stored state be further treated in a pyrolysis process by heating to temperatures of the range of 800 to 900.degree. C., if the coke is aimed to be further refined to carbon black or activated carbon. Further the production rate of condensed products will be low, because only a part of formed pyrolytic gas is led through said condenser unit.
It is therefore an object of the present invention to eliminate the above drawbacks by providing a new and improved method for pyrolytic treatment of organic materials of all kinds.
It is another object of the present invention to provide new and improved equipment for carrying out the method according to the invention.